Conventionally, an assistive device called a sheath, into which a catheter used for diagnosis and treatment is inserted, is used to insert the catheter into a vessel or the like (see, for example, JP-A-9-225035, JP-Y-8-7869, and JP-A-7-51381). The sheath is inserted into a vessel in advance before the catheter is inserted into the vessel. The catheter is then introduced into the vessel by being inserted into the sheath.
In such an operation, as large a hole as an outer diameter of the sheath needs to be bored in the vessel. This operation therefore has some undesirable effects. For example, the operation is not suitable for insertion of the catheter through a relatively thin vessel (such as a radial artery in a wrist region), and the patient suffers pain during the operation.
Recently, therefore, there has been proposed a catheter assembly enabling a catheter to be inserted into a vessel without using a sheath (see, for example, JP-A-2002-143318 and JP-A-2002-143319). Such a catheter assembly has a catheter for diagnosis/treatment (hereinafter simply referred to as “catheter”) such as a guiding catheter used for diagnosis or treatment inside a body, and a dilator to be inserted into the catheter. The dilator has a dilation portion which protrudes from a front end of the catheter and enters a vessel. In the catheter assembly having the above configuration, the dilation portion of the dilator is first to enter the vessel. Then, the catheter is inserted into the vessel together with the dilator. After the catheter assembly is inserted by a predetermined length into a body, only the dilator is pulled out of the body to be removed leaving the catheter behind.